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Rolling update config checker, #24009

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* adds config compatibility check
* doc'ed what happens when joining a cluster not supporting this feature
* added extra docs over sensitive paths
This commit is contained in:
Renato Cavalcanti 2018-02-20 15:47:09 +01:00 • committed by Patrik Nordwall
parent a4e9881a6f
commit c83e4adfea
19 changed files with 4832 additions and 123 deletions
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24
akka-docs/src/main/paradox/cluster-usage.md
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@ -994,3 +994,27 @@ Related config properties: `akka.cluster.use-dispatcher = akka.cluster.cluster-d
Corresponding default values: `akka.cluster.use-dispatcher =`.
@@@
### Configuration Compatibility Check
Creating a cluster is about deploying two or more nodes and make then behave as if they were one single application. Therefore it's extremely important that all nodes in a cluster are configured with compatible settings.
The Configuration Compatibility Check feature ensures that all nodes in a cluster have a compatible configuration. Whenever a new node is joining an existing cluster, a subset of its configuration settings (only those that are required to be checked) is sent to the nodes in the cluster for verification. Once the configuration is checked on the cluster side, the cluster sends back its own set of required configuration settings. The joining node will then verify if it's compliant with the cluster configuration. The joining node will only proceed if all checks pass, on both sides.
New custom checkers can be added by extending `akka.cluster.JoinConfigCompatChecker` and including them in the configuration. Each checker must be associated with a unique key:
```
akka.cluster.configuration-compatibility-check.checkers {
my-custom-config = "com.company.MyCustomJoinConfigCompatChecker"
}
```
@@@ note
Configuration Compatibility Check is enabled by default, but can be disabled by setting `akka.cluster.configuration-compatibility-check.enforce-on-join = off`. This is specially useful when performing rolling updates. Obviously this should only be done if a complete cluster shutdown isn't an option. A cluster with nodes with different configuration settings may lead to data loss or data corruption.
This setting should only be disabled on the joining nodes. The checks are always performed on both sides, and warnings are logged. In case of incompatibilities, it is the responsibility of the joining node to decide if the process should be interrupted or not.
If you are performing a rolling update on cluster using Akka 2.5.9 or prior (thus, not supporting this feature), the checks will not be performed because the running cluster has no means to verify the configuration sent by the joining node, nor to send back its own configuration.
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